Modality-Tunable Exfoliated N-Doped Graphene as Effective Electrolyte Additive for High-Performance Lithium-Sulfur Batteries.

While chemically doped graphene has shown great promise, the lack of cost-effective manufacturing has hindered its use. This study utilizes a facile fabrication approach for modality-tunable N-doped graphene via thermal annealing of aqueous-phase-exfoliated few-layered graphene from a Taylor-Couette reactor. This method demonstrates a high level of N-doping (27 atom % N) and offers modality tunability of the C-N bond without foregoing scalability and green chemistry principles. The resulting N-doped graphene, with varying N content and doping modality, is utilized in the lithium-sulfur battery electrolyte to address low ionic conductivity, lithium polysulfide (LiPS) shuttling, and Li anode instability. The study reveals that higher N content and pyridinic N modality graphene in the electrolyte positively influence battery performance. The results are 2-fold: higher overall N content improves capacity retention (73%) after 225 cycles at 0.2 C, and pyridinic-type nitrogen demonstrates the best performance at high C rates, exhibiting a 4-fold capacity increase relative to the reference cell at 2 C. Further, the computational study validates the adsorption affinity of LiPS to pyridinic nitrogen and improved Li+ mobility on the graphene backbone observed experimentally. This first experimental study on the impact of N-dopant concentration and modality on electrochemical performance provokes insights into tailoring N functionalization to achieve superior electrochemical performance.

Solid-state polymer-particle hybrid electrolytes: Structure and electrochemical properties.

Solid-state electrolytes (SSEs) are challenged by complex interfacial chemistry and poor ion transport through the interfaces they form with battery electrodes. Here, we investigate a class of SSE composed of micrometer-sized lithium oxide (Li2O) particles dispersed in a polymerizable 1,3-dioxolane (DOL) liquid. Ring-opening polymerization (ROP) of the DOL by Lewis acid salts inside a battery cell produces polymer-inorganic hybrid electrolytes with gradient properties on both the particle and battery cell length scales. These electrolytes sustain stable charge-discharge behavior in Li||NCM811 and anode-free Cu||NCM811 electrochemical cells. On the particle length scale, Li2O retards ROP, facilitating efficient ion transport in a fluid-like region near the particle surface. On battery cell length scales, gravity-assisted settling creates physical and electrochemical gradients in the hybrid electrolytes. By means of electrochemical and spectroscopic analyses, we find that Li2O particles participate in a reversible redox reaction that increases the effective CE in anode-free cells to values approaching 100%, enhancing battery cycle life.